The present invention relates generally to an optical disk apparatus for writing information to an information carrier (a recording medium) or reproducing information recorded on the information carrier by using a light beam from a light source, like a laser, more particularly, the present invention relates to an optical disk apparatus that can detect an abnormal state of an actuator when a focusing control or a tracking control is performed.
Now optical disk apparatuses that can record/reproduce information to/from an optical disk (information carrier or recording medium) having a recording layer formed of a phase-change medium or a magneto-optical medium have come into practical use. Such an optical disk apparatus irradiates a recording surface of the optical disk with a light beam converged by a converging lens (an objective lens) included therein so as to cause a phase change or inversion of magnetic polarization in the recording layer, thereby the information can be recorded onto the optical disk. As for the reproduction, the optical disk apparatus can reproduce the information from the optical disk by detecting reflected light from the optical disk.
In the recording/reproduction operation mentioned above, the light beam is to be subjected to a focusing control in order to accurately place a converging point of the light beam on the recording surface of the optical disk. The focusing control is realized by moving the converging lens in a direction substantially perpendicular to the surface of the optical disk so as to move a focus of the light beam in a thickness direction of the optical disk. In the focusing control, a focusing actuator that is composed of a voice coil motor, for example, is used for moving the converging lens. Once the focus of the light beam is positioned on the recording surface of the optical disk, the focusing actuator controls the movement of the converging lens to keep a distance between the recording surface and the converging lens substantially constant (this corresponds to a state where a focusing servo is performed).
In the focusing control, a relatively large driving current may be applied to the focusing actuator continuously because of a breakdown of a circuit included in a focusing servo system or the like. When such a large driving current continuously flows through the focusing actuator over a time period longer than a predetermined time period, a power supplied to the focusing actuator may exceed the maximum rating power thereof, causing overheating of the focusing actuator. This overheating may cause the focusing actuator to be damaged.
As a method for protecting the actuator from being damaged, there is a known method in which the driving of the focusing actuator is stopped when the driving current for the actuator exceeds a predetermined current value (Japanese Patent Publication No. 6-64745, for example). In accordance with the method, it is possible to determine that the focusing actuator is driven abnormally in a case where the current having the magnitude exceeding a predetermined magnitude is continuously applied to the focusing actuator, as shown in FIG. 1A, when the optical disk apparatus begins the operation or the focusing servo is performed. Thus, the damage of the actuator can be prevented.
Moreover, when the focusing servo is performed, a transient disturbance may occur because of a partial waver caused by a local undulation or unevenness of the recording surface of the optical disk generated in a fabrication process of the optical disk, a vibration applied to the optical disk apparatus or the like. In a case where the focusing actuator is driven in order to suppress the aforementioned external disturbance, a driving current shown in FIG. 1B, for example, flows through the focusing actuator. By supplying such a driving current to the focusing actuator, it is possible to make the movement of the converging lens follow the waver of the optical disk, thus maintaining the appropriate focusing state.
However, according to the aforementioned conventional method for protecting the actuator, when the driving current shown in FIG. 1B is supplied to the focusing actuator, it is determined that the driving of the focusing actuator is in the abnormal state at a time at which the current value exceeds the predetermined current value even if the power does not exceed the maximum rating power expressed as the product of a predetermined time period (rating time) and a predetermined current value (rating current), so that the driving of the focusing actuator is stopped. This prevents the supply of the driving current having a necessary magnitude to the focusing actuator, resulting in a failure of the focusing servo.
On the other hand, as a method of protecting the actuator, there is another known method in which the driving current for the focusing actuator is integrated by using a predetermined time constant and the driving of the focusing actuator is stopped when the integration result (that is, the power) exceeds a predetermined value (Japanese Patent No. 2864799, for example). In accordance with this method, it is not determined that the driving of the focusing actuator is in the abnormal state when the driving current shown in FIG. 1B flows through the focusing actuator. Thus, it is possible to continue the focusing servo.
The latter protection method utilizes an integration technique (a signed value integration) in which an output of an integrator is always approximately zero in a case where the driving current goes between a plus side (charging) and a minus side (discharging). This is because this method takes a case of suppressing the disturbance in one direction (a direction in which the converging lens becomes closer to the optical disk or a direction opposite thereto) occurring at a period substantially the same as the rotation period of the optical disk into consideration. In this case, in order to protect the actuator, it is sufficient that the integration result of the current value when the driving current corresponding to such a flash or transient unidirectional disturbance flows through the actuator is obtained. During a period in which no transient disturbance occurs (when the normal servo is performed), the driving current fluctuates between the positive and the negative while having the smaller amplitude. It is preferable according to this conventional protection method that the driving current when the normal servo is performed is not contained in the current integration value used for determining whether or not the condition for protecting the actuator is satisfied.
In recent years, the rotation speed of the optical disk in the optical disk apparatus has been largely increased. However, this causes a problem of occurrence of an external disturbance having a high frequency. It is known that the waver caused when the optical disk rotates contains not only a waver occurring in synchronization with one rotation of the optical disk (a primary component) but also a component N times the primary component (a higher degree component). In a case of rotating the optical disk at 160 Hz to 180 Hz, for example, the primary waver having the frequency of 160 Hz to 180 Hz and a high frequency component (the high-frequency disturbance) having 2 kHz to 3 kHz may be generated. Such a high-frequency disturbance largely influences the focusing servo.
Herein, the influences of the high-frequency disturbance on the focusing servo are described.
FIG. 2 shows loop characteristics of the focusing servo system in the conventional optical disk apparatus. The waver having a lower frequency and a large amplitude, such as the primary component of the waver, is generated in a lower-frequency region (100 Hz or less, for example). Thus, as shown with Line A in FIG. 2, it is necessary to set the loop gain in the lower-frequency region to be a large value so as to improve the ability of following the waver of the optical disk. This enables the focusing actuator to be driven in such a manner that a deviation of the focus from the recording surface is equal to or less than a predetermined level, thereby the focusing control can be performed appropriately. On the other hand, the loop gain is set to be a small value in a higher-frequency region (1 kHz or more, for example). This is because the amplitude of the high-frequency disturbance is small (for example, within a range where a signal can be read from the optical disk) and therefore there is no problem even if the gain of the servo is made small.
When the optical disk is rotated at a higher speed, however, the external disturbance having the quite high frequency is generated. The spectrum of such disturbance is shown in FIG. 2. As the amplitude of such a high-frequency component becomes larger, there arises a necessity of making the loop gain of the focusing servo system relatively larger. Therefore, in the case of rotating the optical disk at the higher speed, the high-frequency disturbance having the large amplitude is suppressed by making the gain (loop gain) of the servo larger, as shown with Line B in FIG. 2, to improve the following ability. Otherwise, the appropriate focusing servo state cannot be maintained because of the high-frequency component of the disturbance, preventing the continuous reproduction/recording operation.
In the case of the larger loop gain, however, the power consumption of the focusing actuator also becomes large. To the focusing actuator, the driving current containing the high-frequency component having the large amplitude, for example, as shown in FIG. 1C, is supplied in order to follow the high-frequency disturbance. Such a current component fluctuates between the plus side and the minus side as the driving current for suppressing the primary waver of the optical disk fluctuates. The current component is always applied to the focusing actuator when the focus servo is performed. This means that a substantially constant additional power is supplied to the focusing actuator.
Therefore, when the optical disk is rotated at the higher speed, the large driving current containing a high-frequency AC component is applied to the focusing actuator, thus the focusing actuator may continue to be driven abnormally. The adverse effect of the AC component contained in the driving current on the focusing actuator becomes larger as the rotation speed of the optical disk increases. The higher-frequency AC component of the driving current increases the power supplied to the focusing actuator.
On the other hand, according to the latter one of the conventional protection methods mentioned above, the AC component of the driving current fluctuating between the plus side and the minus side that is generated when the focusing servo is performed for the optical disk rotating at the higher speed cannot be detected. Thus, it is impossible to determine whether or not the abnormal driving of the focusing actuator occurs. Such a problem does not arise when the optical disk is rotated at a relatively low speed.
Moreover, the conventional optical disk apparatus protects the actuator by stopping the driving of the focusing actuator when detecting the abnormal driving of the focusing actuator. Thus, there is a problem that information recorded on a portion where the abnormal driving is detected cannot be reproduced.
Furthermore, the conventional optical disk apparatus does not have a protection function for a tracking actuator. Therefore, it is impossible to detect an AC component of a large driving current applied to the tracking actuator when the reproduction/recording operation is performed for the optical disk eccentrically rotating at the higher speed, as in the case of the focusing actuator. Accordingly, the abnormal driving of the tracking actuator cannot be detected. The protection of the tracking actuator is also important when the optical disk is rotated at the higher speed.
The invention provides an optical disk apparatus that can stably perform the reproduction/recording operation for the optical disk while protecting the focusing/tracking actuator appropriately.
An inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; a moving means operable to move a converging point of the light beam in a direction substantially perpendicular to a surface of the information carrier; and a focusing controller operable to control the moving means to place the converging point of the light beam at a predetermined position. The focusing controller includes: a converging state detector operable to generate a detection signal corresponding to a converging state of the light beam on the information carrier; a focusing driving means operable to generate a driving signal for driving the moving means based on the detection signal; an integrator operable to integrate a magnitude of a signal corresponding to the driving signal over a predetermined time period; and an abnormal state detector operable to detect an abnormal state of the moving means based on an output of the integrator.
Another inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; a moving means operable to move a converging point of the light beam in a direction substantially perpendicular to a surface of the information carrier; and a focusing controller operable to control the moving means to place the converging point of the light beam at a predetermined position. The focusing controller includes: a converging state detector operable to generate a detection signal corresponding to a converging state of the light beam on the information carrier; a focusing driving means operable to generate a driving signal for driving the moving means based on the detection signal; an integrator operable to integrate a magnitude of a signal corresponding to the detection signal over a predetermined time period; and an abnormal state detector operable to detect an abnormal state of the moving means based on an output of the integrator.
In one embodiment of the present invention, the driving signal is decreased to prevent the moving means from being damaged when the abnormal state detector detects the abnormal state of the moving means.
In another embodiment of the present invention, a loop gain of the focusing controller is decreased when the abnormal state detector detects the abnormal state of the moving means.
In still another embodiment of the present invention, a rotation speed of the information carrier is lowered when the abnormal state detector detects the abnormal state of the moving means.
In yet another embodiment of the present invention, the optical disk apparatus further includes: a second moving means operable to move the light beam in a direction traversing a track formed on the surface of the information carrier; a deviation detector operable to generate a signal corresponding to a positional relationship between the light beam and the track; and a tracking controller operable to control the light beam to scan on the track by driving the second moving means in response to the signal generated by the deviation detector. The abnormal state detector changes a detection threshold value used for detection of the abnormal state in accordance with operation modes of the tracking controller.
Still another inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; a moving means operable to move the light beam in a direction traversing a track formed on a surface of the information carrier; a tracking controller operable to control the moving means to scan the track with the light beam. The tracking controller includes: a deviation detector operable to generate a detection signal corresponding to a positional relationship between the light beam on the information carrier and the track; a tracking driving means operable to generate a driving signal for driving the moving means based on the detection signal; an integrator operable to integrate a magnitude of a signal corresponding to the driving signal over a predetermined time period; and an abnormal state detector operable to detect an abnormal state of the moving means based on an output of the integrator.
Yet another inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; a moving means operable to move the light beam in a direction traversing a track formed on a surface of the information carrier; a tracking controller operable to control the moving means to scan the track with the light beam. The tracking controller includes: a deviation detector operable to generate a detection signal corresponding to a positional relationship between the light beam on the information carrier and the track; a tracking driving means operable to generate a driving signal for driving the moving means based on the detection signal; an integrator operable to integrate a magnitude of a signal corresponding to the detection signal over a predetermined time period; and an abnormal state detector operable to detect an abnormal state of the moving means based on an output of the integrator.
In one embodiment of the present invention, the driving signal is decreased to prevent the moving means from being damaged when the abnormal state detector detects the abnormal state of the moving means.
In another embodiment of the present invention, a loop gain of the tracking controller is decreased when the abnormal state detector detects the abnormal state of the moving means.
In still another embodiment of the present invention, a rotation speed of the information carrier is lowered when the abnormal state detector detects the abnormal state of the moving means.
Yet another inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; and a moving means operable to move a converging point of the light beam in a direction substantially perpendicular to a surface of the information carrier. The magnitude of a focusing control signal is integrated over a predetermined time period, the focusing control signal being used for controlling a movement of the moving means to place the converging point of the light beam at a predetermined position. A driving signal for driving the moving means is adjusted based on a result of the integration.
Yet another inventive optical disk apparatus includes: a light irradiator operable to converge a light beam and irradiate an information carrier with the converged light beam; and a moving means operable to move the light beam in a direction traversing a track formed on a surface of the information carrier. The magnitude of a tracking control signal is integrated over a predetermined time period, the tracking control signal being used for controlling a movement of the moving means to allow the light beam and the track to have a predetermined positional relationship. A driving signal for driving the moving means is adjusted based on a result of the integration.